Tubular halogen cycle incandescent lamps



' July 21, 1970 I J. F. ENGLISH ET AL 3,521,109

TUBULAR HALOGEN CYCLE INCANDESCENT LAMPS Filed April 18, 1968 lnve'n tovsi James F. En cgLish David FLGreeTw b3 01% Their b t' vneg United States Patent 3,521,109 IUBULAR HALOGEN CY (SILE INCANDESCENT LAMP James F. English, Lakewood, and David H. Green, Waite Hill, Ohio, assignors to General Electric Company, a

corporation of New York Filed Apr. 18, 1968, Ser. No. 722,241 Int. Cl. H01j 61/26 US. Cl. 313222 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to electric incandescent lamps comprising a filament sealed in a bulb or envelope, and more particularly to lamps of the halogen regenerative cycle type wherein the tungsten filament is enclosed in a compact bulb or envelope containing an inert fill gas and a halogen, and the walls of which achieve high temperatures during operation of the lamp and wherein the halogen reacts with tungsten particles vaporized from the filament to form a compound which migrates back to the vicinity of the filament where it breaks down to release tungsten for deposition back upon the filament and to release the halogen for repetition of the cycle. Still more particularly, the invention relates to such lamps having elongated tubular envelopes with axially extending filaments and wherein occurs the phenomenon of a thermal diffusion separation of the halogen from the fill gas when the lamp is operated vertically, or even at a small angle from the horizontal. The result is an accumulation of the halogen at one end of the lamp and a deficiency at the other end which leads to a blackening of the said other end of the envelope. 1

Description of the prior art One solution of the problem of thermal diffusion separation of the halogen from the fill gas is to employ a high pressure of the fill gas above a critical minimum amount which differs with the different fill gases and with the filament temperature, as described and claimed in Pat. 3,240,975 to I. F. English and E. G. Zubler. Another solution is the provision within the tubular envelope of a tubular transparent sleeve arranged concentrically between the filament and the envelope and between the normal paths of gas flow upwardly along the filament and downwardly at the envelope Wall. In that manner, the normal thermal diffusion of a halogen like iodine radially toward the envelope wall is blocked by the said sleeve, thereby preventing the downward moving stream of fill gas from carrying the iodine to the bottom of the envelope. The latter arrangement is more fully described and claimed in US. application Ser. No. 565,457 to D. H. Green, filed July 15, 1966, now Pat. No. 3,435,272, assigned to the same assignee as the present case.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an alternative solution for the problem of thermal separa- 3,521,109 Patented July 21, 1970 BRIEF DESCRIPTION OF THE DRAWING The drawing is an elevation of a lamp comprising the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, the lamp illustrated therein comprises a tubular envelope 1 which may be made of heat resistant hard glass or, preferably of fused silica or quartz, having therein an axially extending filament 2 of helically coiled tungsten wire connected by straightened end or leg portions 3 to extremely thin foliated seal portions 4 of molybdenum lead Wires 5 hermetically sealed in flattened pinch seal portions 6 at respective ends of the envelope. The filament is preferably supported at spaced intervals by support members 7 such as spirals or tungsten wire which are attached to the filament and support it from the inner envelope walls. The envelope 1 also contains a filling of a selected combination of inert gas and small amount of halogen compound in accordance with the invention and which may be introduced therein through an exhaust tube, the tipped off residue of which is shown at '8.

The fill gas in lamps of this type may consist of an inert gas such as argon, neon, krypton or xenon at a pressure of at least several hundred torr and preferably from about one to several atmospheres and which may also contain nitrogen admixed therewith, and the halogen may consist of a small amount of iodine, bromine, chlorine or fluorine getter which serves to prevent blackening of the elongated envelope 1 by virtue of the cyclic process described above.

The envelope 1 usually has a diameter amounting to a fraction of an inch, commonly about or /2 inch, or ranging from about 2 to 20 millimeters, and a length at least three times its diameter. For example, a typical 500 watt, volt lamp may have an envelope of 8 mm. internal diameter and an internal length, between pinch seals 6, of about 80 mm. A 1500 watt, 270 volt lamp may also have an internal diameter of 8 mm. and an internal length of about 400 mm.

In accordance with the present invention, the separation of the regenerative getter and the fill gas is effectively decreased to permit operation of the lamp vertically or in any position by selecting a regenerative material and a fill gas which have about the same molecular weight. It will be noted that even if bromine is selected, its molecular weight of about is larger than that of the heaviest of the stated inert gases, namely xenon. The solution, then, is to use chemical compounds containing the regenerative gas atoms with molecular weights approximately equal to those of the fill gas, and at a low pressure of a few torr, for example within the range of about 0.1 to 10 torr.

By way of example, hydrogen bromide with a molecular weight of about 81 may be used in combination with krypton which has an atomic weight of 83.7, thereby leading to a more uniform distribution of the bromine regardless of orientation of the lamp. Similarly, hydrogen iodide may be combined with xenon to provide a mass for hydrogen iodide of about 128 as compared with xenon at about 131. In the case of the hydrogen iodide it may be desirable to use a heat resistant glass such as the known borosilicate or alumino-silicate glasses, since the hydrogen iodide tends to break down at the high temperatures involved, and the hydrogen tends to diffuse through quartz and be lost. However, such is apparently not the case with hydrogen bromide where the lamp retains a colorless appearance thruoghout its life, rather than the brownish color characteristic of elemental bromine.

Other examples of combinations of halogen compound and fill gas of closely matching molecular weights in accordance with the invention, are hydrogen chloride (HCl) with argon, and hydrogen fluoride (HF) with neon.

What We claim as new and desire to secure by Letters Patent of the United States is:

1. In a halogen regenerative cycle incandescent lamp comprising an elongated tubular envelope, a coiled tungsten Wire filament extending axially of said envelope, current supply conductors connected to respective ends of said filament and sealed through said envelope, a filling in said envelope of inert fill gas, and a quantity of halogen in said envelope functioning as a regenerative getter returning to said filament tungsten vapor evolved therefrom during operation of the lamp, the improvement which comprises a selection in said envelope of a halogen compound and a fill gas which have approximately the same molecular weight so that thermal dilfusion separation of the halogen from the fill gas is effectively prevented, and wherein the said halogen compound and fill gas are selected from the group consisting of hydrogen iodide with xenon and hydrogen fluoride with neon, and the said halogen compound is at a pressure in the range of about 0.1 to 10 torr.

2. A lamp as set forth in claim 1 wherein the envelope has an inner diameter greater than 2 mm. and less than 20 mm. and a length exceeding three times the diameter.

3. A lamp as set forth in claim 2 wherein the halogen is hydrogen iodide and the fill gas is xenon.

4. A lamp as set forth in claim 1 wherein the halogen is hydrogen iodide and the fill is xenon.

5. A lamp as set forth in claim 1 wherein the halogen is hydrogen fluoride and the fill gas is neon.

References Cited UNITED STATES PATENTS 3,418,512 12/1968 TJampens et al. 313222 X RAYMOND F. HOSSFELD, Primary Examiner U.S. Cl. X.R. 3 l3179 

